Bi-stable devices are memory elements that store a digital value (i.e., a 1 or a 0). Bi-stable integrated circuit devices are typically latches or flip-flops that utilize a feedback path to maintain the output in a stable state. If the output of a bi-stable device is unbuffered, the device is vulnerable to a failure called back-writing. Back-writing occurs when noise sources such as capacitive coupling, power supply variation, and/or transmission-gate charge sharing cause voltage variations on the output nodes of the bi-stable device that are large enough to switch the logic state stored in the device via the feedback path. Specifically, for the flip-flop to fail, the feedback path must be faster than the output buffer recovery from the noise spike.
In the prior art, flip-flops and latches generally include buffers at the output nodes to eliminate the possibility of back-writing. However, the additional buffers require more silicon area, more power, and introduce more delay in the circuit. An alternative design in the prior art is an unbuffered flip-flop that limits the size of devices in the feedback path to effectively slow down the response of the feedback path to reduce the possibility of back-writing. These flip-flops are limited in their ability to prevent back-writing by the duration of the noise signal. In complementary metal oxide semiconductor (CMOS) integrated circuits, unbuffered flip-flops and latches are highly desirable because they require less silicon area and less power than buffered flip-flops and latches. It would be desirable to provide an unbuffered flip-flop or latch having an improved ability to resist back-writing.